<x-charset iso-8859-1>I don't know if this really helps, but Robertson in his Word-pictures
distinguishes different PISTEUW-s and writes:

"Which had believed him (TOUS PEPISTEUKOTAS AUTWi). Articular perfect active
participle of PISTEUW with dative AUTWi (trusted him) rather than EIS AUTON
(on him) in verse 30. They believed him (cf. 6:30) as to his claims to being
the Messiah with their own interpretation (6:15), but they did not commit
themselves to him and may represent only one element of those in verse
30..."